    (A) Voltage sources are power supply apparatuses for supplying a predetermined level of AC voltage. Conventional voltage sources include those of an electromagnetic coil type and a capacitor division type.
The voltage sources of the electromagnetic coil type are disadvantageous for use as general-purpose equipment because of their heaviness and bulkiness.
The voltage sources of the capacitor division type have a drawback that a desired voltage ratio cannot be provided unless a capacitor having a high capacitance as compared with the capacitance of a load is employed. In use with an inductive load, the voltage sources may cause resonance unless a capacitor having a significantly high capacitance is employed.
It is therefore an object of the present invention to provide a light-weight and compact voltage source. It is another object of the invention to provide a voltage source in which a voltage can easily be set at any desired level.    (B) Conventional convenient-to-use current sources are of a type which includes an iron core and a coil inserted between a power source and a load. The current sources employing the iron core and the coil have a simple circuit configuration, but are disadvantageous because of their heaviness, bulkiness and greater heat loss.
A high frequency switching circuit may be employed for constructing a current source. However, the high frequency switching circuit deals with a frequency much higher than the commercial power source frequency, so that high frequency noises are radiated to adversely affect peripheral apparatuses.
Therefore, there is a demand for developing a current source capable of supplying an AC electric current by employing the commercial power source frequency on an “as is” basis.
If the current source is designed so that the electric current can variably be set at any desired level, the usefulness of the current source will be enhanced.
It is therefore further another object of the present invention to provide a light-weight and compact current source which has a simple construction including a switching element and a capacitor, and features reduced heat dissipation and no high frequency noise.
It is still another object of the present invention to provide a current source in which an electric current can easily be set at any desired level.